I see the plumbers are active so....

I need a plan for piping and operating the cottage heating/DHW system!

Progress so far... gas supply and meter installed. Largest thermal store
I can fit in the space, installed. Upstairs and downstairs underfloor
heating pipework laid and coupled to separate manifolds.

Decisions needed.

Buffer tank? It has been suggested that running the boiler to satisfy a
thermostat calling for heat for say a bathroom circuit will lead to
boiler cycling and inefficient operation. How does one include this in
the control system and how large does it need to be.

The thermal store is probably undersized based on the usual
shower/bathroom number calculations but space limited. With the expected
slow response from underfloor heating, it seems best to prioritise the
DHW.

Chalet bungalow with limited headroom. Pressurised system? System
boiler? Serious lack of knowledge area:-)

Apart from picking the brains in here, is there a useful on line source?

--
Tim Lamb

On Thu, 11 Jan 2018 10:04:22 +0000, Tim Lamb wrote:

Buffer tank? It has been suggested that running the boiler to satisfy a
thermostat calling for heat for say a bathroom circuit will lead to
boiler cycling and inefficient operation. How does one include this in
the control system and how large does it need to be.

Doesn't the thermal store act as a "buffer tank"? The boiler being
controlled by the temperature of the store not by room stats.

A zone, be that DHW or space heating, takes heat from the store. If
the store has enough heat that's all that happens, if it doesn't and
it cools below a given point the boiler is fired up to reheat the
store.

The thermal store is probably undersized based on the usual
shower/bathroom number calculations but space limited.

The store doesn't have to supply the total heat demand in one hit,
once it cools below it's "reheat" point the boiler will be thumping
heat back into it. We have a 300 l store and 30 kW boiler that
reheats at about 2 C/minute, with say a heating zone demanding heat,
Remember the boiler will be taking water from near the bottom of the
store that'll be at 30 to 40 C and returning it to near the top at at
a round 80 C.

With the expected slow response from underfloor heating, it seems best
to prioritise the DHW.

Our store is about 6' tall and 18" ish dia. The DHW coil is across
the top
half, the CH circuits across the lower half. Solar coil, right in the
bottom 8" or so, wood burner from near the top to just above the
solar coil, oil burner top to just above the solar coil (IIRC, but
not grossly wrong).

Stratification in the store means that the DWH coil is always in the
hottest water at the top of the store and the CH can't cool that
significantly without the store getting below the reheat point. The
sensor for the reheat is between the lower DHW level and the upper
CH one.

--
Cheers
Dave.

In message l.net,
Dave Liquorice writes
On Thu, 11 Jan 2018 10:04:22 +0000, Tim Lamb wrote:

Buffer tank? It has been suggested that running the boiler to satisfy a
thermostat calling for heat for say a bathroom circuit will lead to
boiler cycling and inefficient operation. How does one include this in
the control system and how large does it need to be.

Doesn't the thermal store act as a "buffer tank"? The boiler being
controlled by the temperature of the store not by room stats.

A zone, be that DHW or space heating, takes heat from the store. If
the store has enough heat that's all that happens, if it doesn't and
it cools below a given point the boiler is fired up to reheat the
store.

Umm.. I don't know:-) I assume the boiler supplies heat to the thermal
store until the DHW stat. is satisfied. The thermal store water is not
pressurised and simply transfers heat to the DHW demand coil when that
is fed with mains cold water.

There are pumps supplied with each manifold but I assume they only
circulate water round the associated floor heating circuits.

I imagine the boiler pump (or main circulator) would feed either the DHW
top up coil or the heating circuits which could include a buffer store
and thermostat.

The thermal store is probably undersized based on the usual
shower/bathroom number calculations but space limited.

The store doesn't have to supply the total heat demand in one hit,
once it cools below it's "reheat" point the boiler will be thumping
heat back into it. We have a 300 l store and 30 kW boiler that
reheats at about 2 C/minute, with say a heating zone demanding heat,
Remember the boiler will be taking water from near the bottom of the
store that'll be at 30 to 40 C and returning it to near the top at at
a round 80 C.

Ah! I don't have a separate coil for CH.

With the expected slow response from underfloor heating, it seems best
to prioritise the DHW.

Our store is about 6' tall and 18" ish dia. The DHW coil is across
the top
half, the CH circuits across the lower half. Solar coil, right in the
bottom 8" or so, wood burner from near the top to just above the
solar coil, oil burner top to just above the solar coil (IIRC, but
not grossly wrong).

Stratification in the store means that the DWH coil is always in the
hottest water at the top of the store and the CH can't cool that
significantly without the store getting below the reheat point. The
sensor for the reheat is between the lower DHW level and the upper
CH one.

The system suppliers are not very forthcoming and seem to assume you
will use professional installers:-(


--
Tim Lamb

On Thu, 11 Jan 2018 11:49:24 +0000, Tim Lamb wrote:

Doesn't the thermal store act as a "buffer tank"? The boiler being
controlled by the temperature of the store not by room stats.

A zone, be that DHW or space heating, takes heat from the store.
If
the store has enough heat that's all that happens, if it doesn't
and
it cools below a given point the boiler is fired up to reheat the
store.

Umm.. I don't know:-) I assume the boiler supplies heat to the thermal
store until the DHW stat. is satisfied.

You don't have any stored DHW so no DHW stat. To control the DHW
temperature there should be thermostatic mixer valve on the thermal
stores DHW coil output to stop 80+ C water being deliverd to the
taps. DHW is heated on demand by passing through the coil in the
(upper part of the) thermal store.

There are pumps supplied with each manifold but I assume they only
circulate water round the associated floor heating circuits.

Possibly, no pratical experiennce of wet underfloor heating.

The store doesn't have to supply the total heat demand in one hit,
once it cools below it's "reheat" point the boiler will be
thumping
heat back into it. We have a 300 l store and 30 kW boiler that
reheats at about 2 C/minute, with say a heating zone demanding
heat,
Remember the boiler will be taking water from near the bottom of
the
store that'll be at 30 to 40 C and returning it to near the top at
at
a round 80 C.

Ah! I don't have a separate coil for CH.

Neither have I. The water in the store is the same water circulated
around the CH zones, the wood burner and oil burner loops. The DHW
passes through a coil immersed in that water to pick up heat. The
solar thermal has a coil because that loop is heavyly dosed with
glycol to stop it freezing at the collector.

The system suppliers are not very forthcoming and seem to assume you
will use professional installers:-(

Who might not understand it either... ours didn't.

--
Cheers
Dave.

In message l.net,
Dave Liquorice writes
On Thu, 11 Jan 2018 11:49:24 +0000, Tim Lamb wrote:

Doesn't the thermal store act as a "buffer tank"? The boiler being
controlled by the temperature of the store not by room stats.

A zone, be that DHW or space heating, takes heat from the store.
If
the store has enough heat that's all that happens, if it doesn't
and
it cools below a given point the boiler is fired up to reheat the
store.

Umm.. I don't know:-) I assume the boiler supplies heat to the thermal
store until the DHW stat. is satisfied.

You don't have any stored DHW so no DHW stat. To control the DHW
temperature there should be thermostatic mixer valve on the thermal
stores DHW coil output to stop 80+ C water being deliverd to the
taps. DHW is heated on demand by passing through the coil in the
(upper part of the) thermal store.
Yes.

There are pumps supplied with each manifold but I assume they only
circulate water round the associated floor heating circuits.

Possibly, no pratical experiennce of wet underfloor heating.

The store doesn't have to supply the total heat demand in one hit,
once it cools below it's "reheat" point the boiler will be
thumping
heat back into it. We have a 300 l store and 30 kW boiler that
reheats at about 2 C/minute, with say a heating zone demanding
heat,
Remember the boiler will be taking water from near the bottom of
the
store that'll be at 30 to 40 C and returning it to near the top at
at
a round 80 C.

Ah! I don't have a separate coil for CH.

Neither have I. The water in the store is the same water circulated
around the CH zones, the wood burner and oil burner loops. The DHW
passes through a coil immersed in that water to pick up heat. The
solar thermal has a coil because that loop is heavyly dosed with
glycol to stop it freezing at the collector.

The system suppliers are not very forthcoming and seem to assume you
will use professional installers:-(

Who might not understand it either... ours didn't.

Umm.. The thermal store header tank is only marginally above the store.
I thought pumping over issues might necessitate pressurising the boiler
circuit?

I'll pick this up again this evening. Morning spent on SWMBO tax return!


--
Tim Lamb

On Thu, 11 Jan 2018 13:20:19 +0000, Tim Lamb wrote:

Umm.. The thermal store header tank is only marginally above the store.
I thought pumping over issues might necessitate pressurising the boiler
circuit?

The header tank on our store is integral with the store... ie plonked
right on top of it and covered by the same foam insulation. I think
there is a spurt of pump over when one of the circulators starts but
I've not investigated in detail. I doubt there is much if any
insulation between the top of the store and bottom of header tank.
Maybe a bit of wood for strength?

--
Cheers
Dave.

On 11/01/2018 10:04, Tim Lamb wrote:

I see the plumbers are active so....

I need a plan for piping and operating the cottage heating/DHW system!

Progress so far... gas supply and meter installed. Largest thermal store
I can fit in the space, installed. Upstairs and downstairs underfloor
heating pipework laid and coupled to separate manifolds.

Decisions needed.

This store, is it intended to run the CH and the DHW?

Buffer tank? It has been suggested that running the boiler to satisfy a
thermostat calling for heat for say a bathroom circuit will lead to
boiler cycling and inefficient operation. How does one include this in
the control system and how large does it need to be.

If the store is running the CH, then this is a non issue. If you are
running (small) CH zones in isolation, then going for a boiler with a
good modulation range will help it load match under a wider variety of
situations.

The thermal store is probably undersized based on the usual
shower/bathroom number calculations but space limited. With the expected
slow response from underfloor heating, it seems best to prioritise the DHW.

Chalet bungalow with limited headroom. Pressurised system? System
boiler? Serious lack of knowledge area:-)

Anything gravity fed will be poor in this circumstance[1], with the
possible exception of a gravity fed heat bank where its heat is used but
not its water pressure (i.e. it can feed a plate heat exchanger or
internal coil for mains pressure DHW).

Do you have decent cold mains flow rate and pressure?

[1] We had exactly that when we moved in here. DHW header tank was about
5' off the floor of the upstairs living space. That meant even lifting
the shower head too high while rinsing the bath was enough to stop the
flow of water.

I spent some time looking at alternatives (keep in mind I did not have
UFH, and the heatloss rate is far from modern standards), and concluded
that splitting the CH into two zones each with its own stat, and adding
weather compensation would probably get the heating about as efficient
as it was realistically possible to do. That just left DHW to worry
about, and it came down to heat bank or unvented cylinder. Although I
quite liked the idea of the heat bank, I could not do it for anything
close to the price of a decent unvented cylinder.

Went for a system boiler since that would integrate with all the
controls I wanted, and allow split temperature operation (i.e. running
low weather compensated flow temps for the heating when required, but
switching up to high flow temps for cylinder recharging). (I did look at
doing it with a combi - having it heat a cylinder like a system boiler,
but then also using its internal DHW for a kitchen tap to eliminate the
longer dead leg out there, but I could not find a solution that quite
did what I wanted). With hindsight the dead leg to the kitchen seems far
less noticeable now there is copious hot water flow and pressure.

Apart from picking the brains in here, is there a useful on line source?

There is a reasonable amount in the wiki.

http://wiki.diyfaq.org.uk/index.php/...heating_design
http://wiki.diyfaq.org.uk/index.php/..._Water_Systems
http://wiki.diyfaq.org.uk/index.php/...and_Heat_Banks
http://wiki.diyfaq.org.uk/index.php/DIY_Heat_Bank
http://wiki.diyfaq.org.uk/index.php/Unvented_DHW


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , John
Rumm writes

On 11/01/2018 10:04, Tim Lamb wrote:

I see the plumbers are active so....

I need a plan for piping and operating the cottage heating/DHW system!

Progress so far... gas supply and meter installed. Largest thermal store
I can fit in the space, installed. Upstairs and downstairs underfloor
heating pipework laid and coupled to separate manifolds.


Snip
Apart from picking the brains in here, is there a useful on line source?

There is a reasonable amount in the wiki.

http://wiki.diyfaq.org.uk/index.php/...heating_design
http://wiki.diyfaq.org.uk/index.php/..._Water_Systems
http://wiki.diyfaq.org.uk/index.php/...and_Heat_Banks
http://wiki.diyfaq.org.uk/index.php/DIY_Heat_Bank
http://wiki.diyfaq.org.uk/index.php/Unvented_DHW

OK John. I'll have a closer look through the wiki over the weekend and
come back when I have some specific queries.

Currently I am not very clear on the system boiler functions!
We have a Veissman Vitodens100 (Combi) professionally fitted in a granny
annexe. Fitted by their trained plumbers, these come with a long
guarantee so the manufacturer is under consideration. For under floor
and 24 hour occupation, I doubt the value of weather compensation:-)

For a pressurised system with around 800m of 16mm pipe, I wondered
whether the boiler expansion vessel would be adequate and whether a back
up fitted in the buffer tank would be of value?

Oh! Scrub that! I started off trying to avoid safety discharge systems.
Back to trying to find a way to use the boiler mate heating coil as a
buffer store!



--
Tim Lamb

On 12/01/2018 09:50, Tim Lamb wrote:
In message , John
Rumm writes

Currently I am not very clear on the system boiler functions!

You can think of it being a bit like a combi with the DHW capability
removed. i.e. it has a pump, expansion vessel, and most of the controls
required all in one box.

Some also go a step further and have a more programmed understanding of
things like UFH, and can directly control blending valves. ISTR mine
(Vaillant) even has programs for drying your UFH floor screed, by
ramping up temperatures over a few weeks.

Some directly support multiple zones as well.

We have a Veissman Vitodens100 (Combi) professionally fitted in a granny
annexe. Fitted by their trained plumbers, these come with a long
guarantee so the manufacturer is under consideration. For under floor
and 24 hour occupation, I doubt the value of weather compensation:-)

The 24 hour bit would add to the argument for it. However its probably
less relevant for UFH.

For a pressurised system with around 800m of 16mm pipe, I wondered
whether the boiler expansion vessel would be adequate and whether a back
up fitted in the buffer tank would be of value?

800m of pipe is probably significantly less volume of water than a
conventional rad system...

I guesstimate my system has between 150 and 200L of primary water (21
rads), and that is fine on the internal expansion vessel in the boiler.

Oh! Scrub that! I started off trying to avoid safety discharge systems.
Back to trying to find a way to use the boiler mate heating coil as a
buffer store!

With a sealed primary (as would be used by most system boilers, all the
discharge system is built in. You normally (on a wall mounted boiler)
take a pressure relief pipe through the wall and down to low level. If
the system does vent, then it will only typically sump a few litres of
water (being sealed - there is no continuous replenishment of water - so
the damage that can be done is far less)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , John
Rumm writes
On 12/01/2018 09:50, Tim Lamb wrote:
In message , John
Rumm writes

Currently I am not very clear on the system boiler functions!

You can think of it being a bit like a combi with the DHW capability
removed. i.e. it has a pump, expansion vessel, and most of the controls
required all in one box.

Some also go a step further and have a more programmed understanding of
things like UFH, and can directly control blending valves. ISTR mine
(Vaillant) even has programs for drying your UFH floor screed, by
ramping up temperatures over a few weeks.

Some directly support multiple zones as well.

We have a Veissman Vitodens100 (Combi) professionally fitted in a granny
annexe. Fitted by their trained plumbers, these come with a long
guarantee so the manufacturer is under consideration. For under floor
and 24 hour occupation, I doubt the value of weather compensation:-)

The 24 hour bit would add to the argument for it. However its probably
less relevant for UFH.

For a pressurised system with around 800m of 16mm pipe, I wondered
whether the boiler expansion vessel would be adequate and whether a back
up fitted in the buffer tank would be of value?

800m of pipe is probably significantly less volume of water than a
conventional rad system...

I guesstimate my system has between 150 and 200L of primary water (21
rads), and that is fine on the internal expansion vessel in the boiler.

Oh! Scrub that! I started off trying to avoid safety discharge systems.
Back to trying to find a way to use the boiler mate heating coil as a
buffer store!

With a sealed primary (as would be used by most system boilers, all the
discharge system is built in. You normally (on a wall mounted boiler)
take a pressure relief pipe through the wall and down to low level. If
the system does vent, then it will only typically sump a few litres of
water (being sealed - there is no continuous replenishment of water -
so the damage that can be done is far less)

OK John. I'll have a look at Veissman (stainless heat exchanger) system
boilers and come back if I need further explanations.


--
Tim Lamb